New Frontier Key - Labyrinth Dungeon

[Cthulhu]

Quick general question: I have 8,639 awakening soul fragments. Is it better to use them in the "specials" store or redeem some awakening souls for materials? I need a bunch more of the 1* shards to go from 1 purple star awakening to 2 purple stars.

For low level stuff, it's good buying, but for high-level 4* and 5* stuff, just redeem awakening souls, they also drop 5* hearts.